The demands on communications systems are increasing at a tremendous rate. Reliable date transfer at the rates required for applications such as signal processing necessitate the use of optical communications. As these systems become sufficiently complex, the use of optoelectronic integrated circuits (OEIC) is becoming increasingly attractive for cost and performance reasons. In the last several years, significant efforts have been made toward the monolithic integration of optical and electronic devices formed of III-V compounds and alloys thereof to take advantage of the superior optical properties of III-V compounds over conventional silicon material. In particular, GaAs electronic and GaAs/GaAlAs optical devices on GaAs wafers have received considerable attention. These efforts to date have been successful from the standpoint of preliminary concept demonstration but have been limited by the immaturity of GaAs electronic device technology and the quality of the GaAs material itself. Recent progress in obtaining high-quality GaAs on Si substrates offers the potential to overcome these obstacles. The key advantage of GaAs on Si for integrated optoelectronic components is that the electronic circuits can be fabricated in Si wafers. The design and fabrication technology of Si circuits is well developed and the economics of such circuits is very attractive. This approach to monolithic GaAs and Si integration will complement Si electronic circuits with GaAs/GaAlAs optical components.
The essence of monolithic integration technology is not only the ability to grow high-quality GaAs on Si substrates but also the ability to fabricate GaAs and Si devices together on a single chip. The ability to grow high quality GaAs layers on Si substrates has been demonstrated by several groups. The fabrication of GaAs and Si devices together on one chip has also been demonstrated.
Full monolithic integration of interconnected GaAs/GaAlAs double heterostructure Light Emitting Diodes (LEDs) and Si MOSFETs has also been demonstrated (see co-pending U.S. Pat. No. 4,774,205 issued Sept. 27, 1988 to H.K. Choi et al.)
Despite the above, much work remains before full scale commercialization of these approaches can be realized. One of the remaining problems is to find a convenient and reliable method and apparatus for coupling the light to and from the optical devices. In conventional non-integrated structures light is coupled from the lasers via optical fibers aligned with the active laser emitting edge of the optical device. Such alignment is a difficult labor intensive exercise, which if improperly performed, can result in damage to the laser device, or the fiber, or both.